Direct injection engines may provide increased engine performance while at the same time reducing some transient fueling problems associated with port fuel injected engines. For example, injecting fuel directly into a cylinder can reduce or eliminate fuel puddles in intake ports. Further, vaporization of injected fuel can extract heat energy from an incoming cylinder charge so that additional air can enter an engine cylinder and increase the cylinder charge. Thus, direct injection engines may provide certain advantages over port fuel injected engines.
Direct injection engines may, however, have some disadvantages over port fuel injected engines. In particular, direct fuel injected engines may produce soot during some conditions. For example, soot may be formed when injected fuel is partially combusted, and some directly injected fuel may not completely combust during a cylinder cycle when fuel partially vaporizes or condenses in the cylinder. Partial vaporization or condensation of fuel may occur when conditions for combustion change between cylinder cycles. For example, soot may be produced when engine load in changed or when an amount of exhaust gas recirculation (EGR) is changed.
The inventors herein have developed a method for controlling soot produced by a direct injection engine. Specifically, the inventors have developed a method for directly injecting fuel to cylinder of an engine, comprising: in response to a change in load, adjusting start of injection timing away from a first timing and then back toward said first timing to a second timing during the change in load, said second timing different from said first timing.
Soot may be reduced in a direct injection engine by adjusting injection timing in response to a change in engine operating conditions. For example, injection timing can be temporarily advanced for one or more cylinder cycles during a change from a lower engine load to a higher engine load. By first advancing and then retarding injection timing, it may be possible to reduce the amount of fuel that may form on surfaces in the cylinder when fuel is injected. Advancing injection timing may enable fuel to enter the cylinder at a time when the piston is lower in the cylinder so that a larger portion of the injected fuel may vaporize in the cylinder rather than collecting on the piston. The advanced fuel timing can then be returned to an injection timing that is suited for steady-state engine operating conditions. Thus, upon a change in engine conditions, injection timing can be advanced for one or more cylinder cycles and then retarded to a timing that is desirable for steady-state conditions.
The present description may provide several advantages. Specifically, the approach may improve engine emissions by lowering the production of soot. Further, the method can reduce system cost because exhaust gas after treatment devices may be reduced in size. In addition, regeneration of a particulate filter that captures soot exhausted from engine cylinders may be performed less frequently because less soot may be deposited on the filter.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.